Constant conductivity alloys



United States Patent Oflice 3,463,636 Patented Aug. 26, 1969 3,463,636CONSTANT CONDUCTIVITY ALLOYS John R. Ogren, La Palma, Califi, assignorto TRW Inc., Redondo Beach, Calif., a corporation of Ohio No Drawing.Filed Jan. 3, 1967, Ser. No. 606,574 Int. Cl. C22c 5/00 U.S. Cl. 75-1652 Claims ABSTRACT OF THE DISCLOSURE Prior-art constant conductivityalloys, in general, must be confined to a narrow range of temperaturesin order to exhibit constant conductivity. Even within this narrowtemperature range, undesirable deviations may be detected in theconductivity of the prior-art alloys. The priorart alloys of 97.9%gold-2.1% chromium; 84% copper- 12% manganese-4% nickel (manganin); and60% copper-40% nickel (constantan) must be employed within a narrowrange of a few centigrade degrees of ambient temperature in order toexhibit a degree of constant conductivity. Other attempts to produceconstant electrical conductivity materials have involved the use ofcomposite structures in which the conductivity changes that occur indifierent parts of the structure counteract each other giving an overallconstant conductivity to the structure.

Alloys according to this invention, are ternary alloys comprising amajor proportion of a metal selected from the group consisting ofplatinum, rhodium, iridium, palladium, gold, or silver, which is alloyedwith a minor proportion of tungsten, and a minor proportion of rhenium.These ternary alloys exhibit only slight deviation in conductivity overtemperatures ranging from 70 to 500 K. Constant conductivity with nodeviation has been obtained over a temperature range of 100 K. to about220 K. using these alloys.

While alloy formation may be accomplished by melting the three separatemetals, a shorter way takes advantage of available alloys containingtungsten-% rhenium. By using the tungsten-rhenium alloy, preparation ofthe constant conductivity alloys is somewhat simplified since themelting and solution of only two solid ingredients is necessary. Thus,alloy production simply constitutes the melting of 70% to 90% by weightof one of the noble metals with 10 to by weight of the tungsten-25%rhenium alloy. Alloy preparation is accomplished by standard artprocedures. The metal components are placed in a water-cooled coppercrucible and melted in an electric-arc furnace under an inert gas. Toimprove alloy homogeneity, the alloy specimens are remelted severaltimes.

The following table shows a comparison between priorart constantconductivity alloys and the constant conductivity alloy of thisinvention.

Temperatureindependent resistivity Temperature value, microrange for aMaterial ohm-cm. a( C.)- value K.

70% Pt-22.5%W-7.5% Re 11, 200 -0 100-220 97.9% Ail-2.1% Cr.. 32 0.1X10-291-308 84% Cu-12% Mn-4% Ni (manganin) 10 (l0- near 298 Cu-40% Ni(constantan) 44 8X10- near 298 1 do =I a p (17 '=resistivity of samplematerial (ohm-cm). T =Ternperature (K.).

From the table it is seen that the temperature range over which theresistivity of the new alloy remains constant is much more extensivethan that of competitive alloys. The a-values for the competitive alloyare seen .to be applicable only to a narrow temperature range.

If a wider temperature range is considered for the competitive alloys,then the average a-values also increase. Furthermore, because of highresistivity, it will be possible to make with alloys of this invention,small compact constant conductivity components which will minimize strayelectromagnetic interactions.

Ductility of these ternary alloys is widely variant. Heat treatments maybe employed to increase the ductility of the alloys. Where this heattreatment is not desirable because of adverse effects on the electricalproperties, constant conductivity devices may be fabricated by standardart techniques of painting a slurry of the alloy components on a ceramicsubstrate and heating to produce alloy formation.

Alloys of this invention may be soldered, brazed, and welded to allforms of electrical conductors by standard art techniques.

I claim:

1. A constant conductivity ternary alloy consisting essentially of -90weight percent of a metal selected from the group consisting ofplatinum, rhodium, iridium, palladium, gold, and silver; 7-23 weightpercent tungsten; and 2-8 weight percent rhenium, the alloy possessing arelatively constant conductivity over .a temperature range of from about70 to about 500 K.

2. An electrical resistor comprising an alloy consisting essentially of70 weight percent platinum, 22.5 weight percent tungsten, and 7.5 weightpercent rhenium, the alloy possessing a relatively constant conductivityover a temperature range of from about 70 to about 500 K.

References Cited UNITED STATES PATENTS 1,407,525 2/1922 Fry 1721,978,198 10/1934 Handforth 75172 X 2,300,286 10/1942 Gwyn 75--165 X2,344,597 3/1944 Chaston et al 75-172 2,370,242 2/ 1945 Hensel et al75l65 2,391,458 12/1945 Hensel 75172 FOREIGN PATENTS 1,383,618 11/1964France.

CHARLES N. LOVELL, !Primary Examiner U.S. Cl. X.R.

